1. Field of the Invention
The present invention relates to shields for the light-diffusing lenses of luminaires.
2. Prior Art
Lenses are often provided to diffuse light from the light-producing means of a luminaire and to cover such light-producing means. Conventionally, light-diffusing lenses are made of glass and, hence, are subject to vandalism breakage. Such breakage necessitates frequent replacement of light-diffusing lenses and also subjects persons in the area of the luminaire to injury due to broken glass.
Light-diffusing lenses have been made of a synthetic such as polycarbonate resin which has greater impact resistance and, consequently, is less subject to breakage than glass. However, forming an impact resistant synthetic into the complex shape and structure required to diffuse light into a desired pattern is expensive. In addition, there has been a trend toward use of higher output light sources, particularly in outside luminaires such as streetlights. Such higher output light sources produce more heat and ultraviolet radiation which can discolor and even deform synthetic lenses, especially when the lenses are located close to the luminaire light-producing means where such lenses are most effective to diffuse light. Thus, exotic and expensive synthetics have been used to form light-diffusing lenses having high impact strength, heat resistance and dimensional stability. Even lenses formed of such exotic synthetics will become discolored if left in place for an extended period.